1. Field of the Invention
The present invention relates to a sheet supply apparatus for supplying record sheet to an image forming apparatus, and more particularly to a sheet supply machine having a vertically movable sheet supplying table supporting a plurality of record sheets stacked thereon in which an image forming position to the record sheet can be adjusted by moving the sheet supplying table right and left.
2. Description of the Related Art
An image forming apparatus for forming an image on record sheets, for example, record sheets for general use, uses the record sheets by loading the record sheets on a sheet supply table. Particularly, in the case of a stencil printing machine, high-speed printing can be carried out since printing operation is carried out by mounting a stencil sheet on a printing drum situated inside the machine and rotating the printing drum. In correspondence therewith, there is constructed a constitution in which a fairly large number of record sheets is loaded on the sheet supply table and the large number of the record sheets can be continuously supplied in a short period of time in correspondence with printing speed.
The sheet supply table is constituted such that the topmost record sheet disposed at sheet supply position is supplied to a print section situated inside the printing machine one by one. A scraper roller (sheet supply roller) of the sheet supply section is provided at the sheet supply position and record sheet can be continuously supplied to the inside of the apparatus by rotating the scraper roller.
Further, there is constructed a constitution in which the sheet supply table is controlled to elevate in correspondence with supply of the record sheet and the topmost record sheet is always brought into contact with the scraper roller.
According to the record sheet, a position thereof in the left and right direction (width direction orthogonal to a transfer direction) is made variable in supplying the record sheet from the sheet supply table to the print section to thereby enable to move an image forming position in the left and right direction on the record sheet. For example, in the case of a stencil printing machine, by making variable a transfer position in the left and right direction of the record sheet relative to the printing drum, a contact position of the record sheet relative to an image position of stencil sheet mounted to the printing drum can be made variable in the left and right direction, so that the image forming position on the record sheet can be moved in the left and right direction.
FIG. 9 is a perspective view showing a sheet supply apparatus. A sheet supply table 50 loaded with the record sheets is provided with a dial 51 for moving the sheet supply table 50 in the left and right direction. By manually adjusting the dial 51, a screw shaft 52 is rotated, a nut portion 53 fixed to the sheet supply table 50 is moved in the left and right direction, thereby moving the sheet supply table 50 in the same direction. Thus, an image forming position on a record sheet P can be adjusted to move in the left and right direction.
The topmost one of the record sheets P loaded on the sheet supply table 50 is brought into contact with a scraper roller 57a of sheet supply means 57 provided above the sheet supply table 50 and the record sheet is supplied one by one from the topmost sheet to a print section by rotating the scraper roller 57a.
The sheet supply table 50 is constituted such that the sheet supply table 50 is controlled to elevate gradually in compliance with supply of the record sheet P and the topmost record sheet P is always brought into contact with the scraper roller 57a and can be supplied to the print section.
However, according to the above-described constitution, if the sheet supply table 50 is moved while the scraper roller 57a contacts the record sheet P for adjusting the image forming position on the record sheet P in the left and right direction, the record sheet P is supplied in an oblique direction by being rubbed with the scraper roller 57a, thereby causing sheet supply jamming in next printing operation. Further, the scraper roller 57a is also damaged. This accelerates deterioration in printing performance of the sheet supply apparatus.
Further, a conventional printer is constituted such that the left and right movement can be conducted regardless of printing operation. Therefore, if the sheet supply table is moved in the left and right direction during printing, conveying force may be exerted in an oblique direction on the record sheet, thereby causing record sheet jamming.
Then, it is possible that the sheet supply table is electrically moved in the left and right direction by means such as a motor instead of the manual operation stated above. However, the above-mentioned problems cannot be solved at all merely by adopting such constitution that the sheet supply table is moved in the left and right direction by motor power. Additionally, if the motor is energized while the scraper roller contacts the record sheet; excessive electric power is consumed due to friction between the scraper roller and the record sheet in comparison with the case where no friction occurs therebetween. This deteriorates electrical efficiency and leads to overheating and life-time deterioration of the motor